The major thrust of this project will continue to be the development of a comprehensive model for the interactions of Na ion and Ca ion in smooth muscle. Specifically, we plan to investigate the effect of alterations in extracellular and intracellular (Na ion) on cellular Ca2 ion content, 45Ca influx, 45Ca efflux, tension, and membrane potential using techniques which have been developed in this laboratory. These parameters will be used to study intracellular Ca2 ion compartmentalization. We will also be involved in studying the phenomenon of ouabain-mediated inhibition of spontaneous and stimulated activity in guinea pig taenia coli. In addition, 45Ca flux experiments will be used to establish the presence of a Ca-ATPase in the plasmalemma of taenia coli and rabbit aorta and to characterize the kinetics of these fluxes. Ultimately, we hope to determine the cellular processes responsible for Ca2 ion extrusion in both intestinal and aortic smooth muscle.